The most widely used method of melting iron for foundry practice is through the use of a cupola. With the use of a cupola, coke, a fluxing material such as limestone, and metallic material are charged into the cupola. The coke is ignited and air is introduced into the sides near the bottom of the cupola and blasts upwardly through the burden to generate an intense heat. The molten metal trickles downwardly through the charge and coke bed and is collected in a well at the bottom of the cupola while molten slag composed of coke ash and non-combustible materials floats on the molten metal in the well.
In the production of iron for foundry practice, the metallic charge generally consists of scrap castings and returns, pieces of steel scrap, cast iron scrap, pig iron and ferrous alloy.
The coke as used in the charge is a high quality metallurgical grade produced from low sulfur coal, which is a relatively expensive material. Coke breeze, on the other hand, which consists of fine granular material from coke, is relatively inexpensive and is normally discarded. Coke breeze itself cannot be charged in the cupola since the air blast and intense heat would immediately consume the coke breeze and blow it out of the cupola with little or no heat produced.
Similarly, small particles of metal scrap cannot be charged into the cupola. Small metal particles, as in the case of the coke breeze, would be blown out of the cupola and/or oxidized with little or no resulting yield of molten metal.